Are you talking about text size in an X window or the console text on boot up before X starts?
If you are referring to the size in X windows, see post above. If you are referring to the latter then you need to look into framebuffer support. If you have the linux kernel source installed then look in the directory /usr/src/linux/Documentation/fb for more help. A goggle search for framebuffer, should also help.
If you use lilo you may see stuff like:
Code:
# VESA framebuffer console @ 1024x768x32k
vga="791"
In your lilo.conf file. Comment out the "vga=normal" and uncomment the resolution you want to use. If you have fb support built into the kernel it should work.
If you use the fb stuff when you boot it may cause problems with X picking its own resolutions. I think that is why MD turns it off once Linux is installed.
edit. - screwed up code tags.